The unit begins with a discussion about what people should and should not drink when they’re thirsty. Students share ideas and the teacher probes for initial ideas without evaluating. The story about the three boys is introduced via slides and a video news clip. Students draw & share initial ideas & questions about why someone can’t drink saltwater to stay alive and what might be happening inside the boys’ bodies over time.

Students generate a list of ideas about what they need to know to complete the challenges:

1. design an oral rehydration therapy (ORT) to treat a severely dehydrated person
2. create a pocket guide to making an ORT
3. be able to explain scientifically why your solution works

Pre-unit-ORT-challenge-ideas

After each concept or activity in the unit, we check back to see how what we have learned relates to the oral rehydration solution. Students take quizzes throughout the unit to assess understanding of content: calculating solution concentration, creating solutions of specific concentrations, and various kinds of membrane transport (osmosis, diffusion, active/passive transport).

Students use the information from the lessons and a final reading to design their oral rehydration solution. Each group creates an index card containing both step-by-step visual and written directions for making the solution, as well as an explanation of what evidence the group members have that their solution will effectively treat dehydration.

Differentiating the final product:

Assign each student/group a different sized container to make their solution – for example, a 1 L Nalgene bottle, a 12 oz soda can, a 20 oz empty plastic water bottle, etc. Students must take the container’s volume into account as they calculate the concentration of their solutions. More advanced students/groups can be assigned containers that require unit conversions and whose size are not round numbers (12 oz, 357 mL). A 1 L container makes the calculations more straightforward.

Additional supports for students with disabilities or students learning English:

Conversion Problems-with-molarity-color-coded-v3solutions membranes vocab list

solutions membranes vocab list

Here’s what I really enjoy about this unit:

Most students know that saltwater is bad to drink, but they typically do not understand the biology and chemistry concepts behind it. This unit showcases the connections between biology and chemistry in the human body, and there are many places in it to connect to health care professions and everyday health understandings. For example – why aren’t IV solutions made of pure water? How can you die of water poisoning? What are the “electrolytes” advertised in sports drinks?

Here’s what I’m still working on making better about this unit:

The content standards require that students have a high level of skill with molarity calculations and creating solutions. To get to this level, we have to spend a few days practicing problems, which means departing for a while from the problem context. I’m always looking for ways to keep the story context alive and continually threaded through the work.

Here’s what I really enjoy about this unit:

Here’s how this unit could help me learn more effectively:

During the unit, we introduce multiple authentic contexts for treating dehydration – childhood deaths from diarrhea/dehydration in developing countries, treating yourself or others in a case of food poisoning, and rehydrating after intense physical activity.  Medical professionals must also calculate solutions and understand effects of solution concentration on living cells when administering and prescribing medication.

Students create their own solution design, along with directions and corresponding to a rubric that grades not only on content but on usability. Creating the solution requires students to integrate and apply their ideas, making this assessment also an authentic measure of their understanding and skills in context.

Throughout the unit, the material is connected to students’ own experiences with exercise and health, and their ideas are sought out. In the final challenge, students design their own solutions, with a minimum of teacher intervention.

Students build their own expertise and draw on the expertise of others in their work. It would be great to bring in a parent or other community member with health care expertise to share how a knowledge of solution concentrations and cell membrane transport is important in their work. This same expert could support students as they make their final products – or perhaps an expert in global health who could give advice about how to communicate information on the index card for people in developing countries, where dehydration from diarrhea and other diseases is a significant cause of death. Students could help identify people or organizations with this expertise.

The phenomenon of feeling thirsty and getting “dehydrated” is one that virtually all students are familiar with and have an intuitive understanding of. Connecting the content to student experience increases its relevance. A focus on impacts of dehydration and diarrhea in developing countries connects this topic to global issues, as well.

Students work together to solve the final challenge of designing their solution. A variety of different skills are required, including reading and comprehending scientific text, doing mathematical calculations, and “translating” a technical procedure into terms that can be easily understood and used. Students may work in groups of four or in partners; working in partners allows for greater engagement of each student.

Students are held accountable for correctly using key scientific terms, such as osmosis, diffusion, molarity, solute, hypertonic, hypotonic, and isotonic. The index card challenge also requires them to practice communicating scientific information in practical, everyday language.